1. Field of the Invention
The present invention relates generally to video signal generating apparatus and more particularly is directed to a video signal generating apparatus capable of generating a video signal which is suitable for being recorded on a video tape recorder (VTR) used in a high speed video system in which a moving object at high speed is picked up by a television camera and the picked up output is recorded on the VTR.
2. Description of the Prior Art
A high speed film camera has hitherto been proposed to pick up and to record an object moving at high speed. This high speed film camera, however, has a defect that the object moving at high speed, which is picked up and recorded by such camera, can not be reproduced immediately. To remove the above defect, various researches and developments have been made in which the object moving at high speed is picked up by a television camera, recorded by a VTR or the like and then reproduced immediately.
As is known well, it takes 1/60 second at minimum for an ordinary television camera to convert one sheet of picture (one field) to an electrical signal. Therefore, it is impossible for the television camera to pick up an object which moves at speed faster than 1/60 second.
To solve this problem, a technique is disclosed in, for example, the publication document of the Japanese patent application examined NO. 26416/1977 in which the visual field of an image pickup tube is divided into a plurality of sections, the whole of an object is placed in each one section of the divided sections and the object image on the image pickup tube is scanned during the scanning period of time corresponding to each section to thereby enable the object moving at high speed to be picked up.
Further, in the publicated document of the Japanese patent application examined, NO. 13631/1980, there is disclosed a technique in which the optical image of an object is sequentially projected onto a plurality of image pickup tubes having accumulation effect at every constant interval during a constant time period, and the picked-up or video signals from the respective image pickup tubes are respectively supplied to a plurality of recording apparatus to thereby successively record the time image of the object moving at high speed.
However, according to the technique disclosed in the publicated document of the Japanese patent application examined, NO. 26416/1977, since the visual field is substantially narrowed, only the image of the periphery of the moving object is obtained. Also since the movable range of the moving object is confined within the area of the divided one section, this technique is not suitable for general use. Moreover, according to the technique disclosed in the publicated document of the Japanese patent application examined, NO. 13631/1980, since a plurality of image pick-up elements, each having accumulation effect, and a plurality of recording apparatus are required, the arrangement thereof becomes complicated, which then becomes significantly inconvenient in practical use.
In addition, apart from the above techniques, other technique may be considered that a video signal picked up by a television camera at the scanning speed of N (N is an integer of 2 or above) times higher than the ordinary scanning speed, namely, the scanning speed for obtaining the standard television signal is directly recorded by using a VTR. In this case, however, since the high speed video signal picked up by the television camera having the scanning speed N times the normal scanning speed is recorded with the high speed being remained as it is, the recording band must be increased N times the normal recording band. As a result, the revolution number of the rotary head must be increased N times the normal revolution number, the carrier frequency of the FM modulation (frequency-modulation) for the video signal must be increased N times the normal carrier frequency and the signal processing in the base band must have the characteristic N times the normal characteristic. Further, in order to establish the compatibility by making the inclination angle of the recorded track or the like comply with the normal recorded pattern, the tape transport speed must be increased N times the normal tape transport speed.
As described above, when the video signal recorded at the speed N times the normal speed is reproduced by the VTR having the normal revolution speed of the rotary head and the normal tape transport speed, the object moving at high speed can be visually perceived. In this case, it becomes quite difficult to ensure the characteristic of the recording and reproducing circuit such as the corresponding relation between the emphasis upon recording and the deemphasis upon reproducing and the stability of the frequency of the frequency-modulated signal, etc. Even if the signal processed in the base band N times the normal base band upon recording is processed in 1/N time upon reproducing, it is quite difficult to ensure various characteristics. Moreover, when the carrier frequency of the FM modulation for the recording signal becomes N times the carrier frequency of the normal VTR, the impedance of the rotary head, characteristic of a rotary transformer and the like cause serious problems so that in practice it becomes impossible to construct a system having a large value of N.
Furthermore, if the revolution number of the rotary head is changed between the recording mode and the reproducing mode, a so-called air film layer between the rotary head drum and the tape is changed in thickness. As a result, the tracing condition of the head on the tape is made different and also the contact pressure of the head with the tape is changed so that the reproducing sensitivity may be lowered.
On the other hand, such a system is known well that a high speed video signal can equivalently be obtained by delaying the output from the television camera having the normal standard scanning speed by a predetermined timing each. However, in this case, there are then defects that the number of the video equipments operating at normal speed is increased and that a mechanism having complicated arrangement is required.